The present invention relates generally to disc brake systems for motor vehicles and more particularly to a method of repairing disc brake calipers incorporated in such systems.
Disc brake systems typically comprise a master cylinder which operates to supply hydraulic or brake fluid under pressure to calipers mounted adjacent the vehicle wheels, in response to depression of the brake pedal by the vehicle operator. The caliper includes a housing having one or more pistons movably disposed within a cylinder provided therein, the piston or pistons being operative to move a pair of disc brake pads into engagement with opposite axially facing surfaces of a rotor which is secured so as to rotate with the vehicle wheel, so as to exert a braking force thereon. In some systems, a single piston is provided and the caliper housing is movable in an axial direction with respect to the rotational axis of the wheel so as to exert a braking force on opposite sides of the rotor. In other systems, the caliper may be fixedly secured to associated support structure and two or more pistons provided on opposite sides of the rotor which are designed to simultaneously advance the pads into engagement with the rotor.
In one form of caliper presently in use on a number of vehicles and with which the present invention is principally concerned, the piston has an annular groove provided thereon within which a seal is disposed which sealingly engages the sidewall of the cylinder so as to prevent fluid leakage therefrom. This seal must be located adjacent the inner edge of the piston in order to maintain a sealing relationship with the cylinder sidewall as the piston is moved outwardly therefrom both during actuation of the brakes and as the pads are worn down through use. Thus, when the pads are new and the piston is normally positioned substantially fully within the cylinder, a significant portion of the cylinder sidewall is located outwardly from the sealed brake fluid containing chamber.
While most disc brake calipers also include dust boots extending between the outer end of the piston and the outer edge of the caliper, they have not proven totally effective in preventing contaminants from contacting the exposed cylinder walls. Thus, when repairing disc brake systems utilizing seals mounted on the piston, it has frequently been found that the cylinder walls have become corroded and pitted to the extent that repair thereof cannot safely be effected. It may then become necessary to replace the entire caliper housing in order to return the brake system to a reliable operating condition. This replacement of the caliper housing in many cases represents a significant increase in the cost of the brake repair. This is particularly true in those systems using multiple piston type calipers as both inner and outer housings may need to be replaced. Further, as the automobile using this type of caliper becomes older, it may very well become impossible to obtain suitable replacement castings which will fit the particular vehicle without potentially extensive and possibly very costly modification to the mounting arrangement therefor.
Accordingly, the present invention provides a method of repairing such disc brake calipers which enables the existing caliper housing to be reused substantially without concern as to the degree of pitting of the cylinder walls while still providing an extremely reliable fully operational brake system. Because the repair method allows the existing caliper housing to be reused, the cost of repairing such system will be greatly reduced. The present method requires a machining operation be performed on the caliper housing to provide a seat in the cylinder sidewall for the piston seal. The piston is then replaced with a piston having a relatively smooth sidewall adapted to sealingly engage the seal provided in the cylinder sidewall. Because the seal no longer is movable along the sidewalls of the cylinder but rather is stationary being fitted within the machined seat, the presence of an imperfect cylinder sidewall as a result of such pitting will not affect the integrity of the seal thus created with the piston. Further, because the cost of replacement pistons is relatively small as compared to caliper housings, future repairs of the system may be accomplished at even lower costs thus affording substantial savings over the life of the vehicle. Additionally, because the new seal will be positioned adjacent the outer end of the cylinder, substantially the entire cylinder wall will be positioned within the sealed brake fluid containing chamber and thus fully protected from any further degradation due to contact with corrosive contaminants or the like. This repair method may be particularly advantageous to owners of older vehicles for which obtaining of replacement caliper housings may be extremely difficult or even totally impossible.
Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying drawings.